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docs: 新增No38和No326题解
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‎leetcode刷题/README.md

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- [No.21 合并两个有序链表](https://github.com/Mayandev/javascript_algorithm/blob/master/leetcode%E5%88%B7%E9%A2%98/note/No21_merge-two-lists.md)
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- [No.26 从排序数组中删除重复项](https://github.com/Mayandev/javascript_algorithm/blob/master/leetcode%E5%88%B7%E9%A2%98/note/No26_remove-duplicates.md)
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- [No.36 有效的数独](https://github.com/Mayandev/javascript_algorithm/blob/master/leetcode%E5%88%B7%E9%A2%98/note/No36_isvalid-sudoku.md)
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- [No.38 报数](https://github.com/Mayandev/javascript_algorithm/blob/master/leetcode%E5%88%B7%E9%A2%98/note/No38_count-and-say.md)
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- [No.48 旋转图像](https://github.com/Mayandev/javascript_algorithm/blob/master/leetcode%E5%88%B7%E9%A2%98/note/No48_rotate.md)
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- [No.66 加一](https://github.com/Mayandev/javascript_algorithm/blob/master/leetcode%E5%88%B7%E9%A2%98/note/No66_plus-one.md)
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- [No.122 买卖股票的最佳时机 II](https://github.com/Mayandev/javascript_algorithm/blob/master/leetcode%E5%88%B7%E9%A2%98/note/No122_max-profit.md)
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- [No.8 字符串转换整数 (atoi)](https://github.com/Mayandev/javascript_algorithm/blob/master/leetcode%E5%88%B7%E9%A2%98/note/No8_my-atoi.md)
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- [No.14 最长公共前缀](https://github.com/Mayandev/javascript_algorithm/blob/master/leetcode%E5%88%B7%E9%A2%98/note/No14_longest-common-prefix.md)
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- [No.28 实现 strStr()](https://github.com/Mayandev/javascript_algorithm/blob/master/leetcode%E5%88%B7%E9%A2%98/note/No28_str-str.md)
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- [No.38 报数](https://github.com/Mayandev/javascript_algorithm/blob/master/leetcode%E5%88%B7%E9%A2%98/note/No38_count-and-say.md)
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- [No.125 验证回文串](https://github.com/Mayandev/javascript_algorithm/blob/master/leetcode%E5%88%B7%E9%A2%98/note/No125_is-palindrome.md)
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- [No.242 有效的字母异位词](https://github.com/Mayandev/javascript_algorithm/blob/master/leetcode%E5%88%B7%E9%A2%98/note/No242_is-anagram.md)
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- [No.387 字符串中的第一个唯一字符](https://github.com/Mayandev/javascript_algorithm/blob/master/leetcode%E5%88%B7%E9%A2%98/note/No387_first-uniq-char.md)
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# No.326 3的幂
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给定一个整数,写一个函数来判断它是否是 3 的幂次方。
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## 示例
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示例 1:
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```
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输入: 27
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输出: true
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```
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示例 2:
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```
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输入: 0
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输出: false
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```
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示例 3:
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```
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输入: 9
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输出: true
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```
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示例 4:
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```
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输入: 45
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输出: false
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```
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## 解题思路
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将输入的数n一直除以3,如果是 3 第次幂,则最后的结果一定为1。
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代码如下:
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```javascript
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/**
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* @param {number} n
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* @return {boolean}
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*/
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var isPowerOfThree = function(n) {
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if (n == 0) {
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return false;
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}
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while (n != 1) {
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n = n / 3;
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if (n == 0) {
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return false;
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}
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}
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return true;
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};
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```
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# No.38 报数
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难度: `easy`
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报数序列是一个整数序列,按照其中的整数的顺序进行报数,得到下一个数。其前五项如下:
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```
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1. 1
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2. 11
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3. 21
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4. 1211
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5. 111221
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```
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1 被读作 "one 1" ("一个一") , 即 11。
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11 被读作 "two 1s" ("两个一"), 即 21。
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21 被读作 "one 2", "one 1" ("一个二" , "一个一") , 即 1211。
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给定一个正整数 n(1 ≤ n ≤ 30),输出报数序列的第 n 项。
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注意:整数顺序将表示为一个字符串。
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## 示例
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示例 1:
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```
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输入: 1
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输出: "1"
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```
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示例 2:
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```
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输入: 4
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输出: "1211"
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```
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## 解题思路
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一次此看题目一脸懵逼,需要多读几遍题目。
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还是用正则表达式来做,全局匹配数字,且数字连续相同。
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代码如下:
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```javascript
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/**
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* @param {number} n
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* @return {string}
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*/
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var countAndSay = function(n) {
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let prev = '1'
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for(let i = 1; i < n; i++){
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prev = prev.replace(/(\d)1円*/g, item =>`${item.length}${item[0]}`)
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}
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return prev
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};
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```

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